Portable filtering systems such as U.S. Pat. No. 4,298,475 to Gartner are known which provide an elongate tube through which water is to be drawn in the manner of a straw. Such filtering systems suffer a number of disadvantages. Firstly, they typically require very strong suction to draw water through them with the result that they are only really suitable for emergency use and cannot conveniently be used to drink fluids. Secondly, the tubes are of a relatively complex structure and are difficult to manufacture.